1. Field of the Invention
The present invention relates to a method for manufacturing a ceramic substrate, particularly to a method for manufacturing a ceramic multilayer substrate capable of surface-mounting an active member such as a semiconductor integrated circuit member and a passive member such as a capacitor and an inductor.
2. Description of the Related Art
Ceramic multilayer substrates for mounting chips of electronic members such as semiconductor integrated circuit members (semiconductor devices) as well as chip capacitors and chip inductors are desired to have a highly integrated wiring among high-precision integrated passive members in order to mount the semiconductor devices and the chips of the electronic members in high density. In addition, a low temperature firing type multilayer ceramic green sheet has been developed for complying with ever growing recent requirements of highly integrated packaging and high operation frequencies, wherein a plurality of insulation ceramic green sheets having a relative dielectric constant of 15 or less, on which conductor patterns comprising low resistance materials such as Ag, Agxe2x80x94Pd, Cu and Au are formed, are laminated, and the laminated ceramic green sheets are fired all at once at a temperature as low as 1000xc2x0 C. or below.
Japanese Unexamined Patent Application Publication No. 5-163072 discloses a method for enabling a highly integrated wiring of the ceramic multilayer substrate, wherein a multilayer ceramic body is subjected to firing while applying a relatively large pressure from the upward and downward of the non-sintered ceramic body. Japanese Unexamined Patent Application Publication No. 4-243918 also discloses a method comprising the steps of: laminating and press-bonding constraint ceramic green sheets, which are not sintered under the firing conditions of the non-sintered ceramic body, on both upper and lower major surfaces of the non-sintered ceramic body prepared by laminating a plurality of ceramic green sheets capable of being fired at a low temperature; firing the ceramic green sheets under a sintering condition of the non-sintered ceramic body; and peeling and removing non-sintered layers derived from the constraint ceramic green sheets.
According to the methods described above, the ceramic multilayer substrate can be formed with a quite high dimensional accuracy, because firing contraction along the directions on the plane of the non-sintered ceramic body, or along the directions on the X-Y plane of the substrate, may be sufficiently suppressed. In other words, the highly integrated wiring hardly causes short-circuits while allowing various kinds of packaging members to be mounted with high precision in the ceramic multilayer substrate obtained.
However, a special equipment for firing under a pressure is required in the former method described above since the multilayer ceramic body is fired while applying a relatively large pressure, leaving a problem in the facility cost and manufacturing efficiency. Although a pressure is not always required for firing in the latter method, it is a problem that the multilayer ceramic body is liable to be warped due to differences of the degree of integration of wiring and the contraction behavior during firing between the upper layer and lower layer relative to the center face located at an equal distance from one major surface and the other major surface of the non-sintered ceramic body.
The number of input-output (I/O) terminals for mounting on and connecting to a mother board has been rapidly increased in the ceramic multilayer substrate as the wiring pattern is highly integrated in recent years. Also, the multilayer ceramic body is required to have highly integrated and accurate circuit elements such as capacitors and inductors since a number of highly precise circuit elements are needed for multi-functional and high performance ceramic multilayer substrate. Under these circumstances, a difference in the degree of contraction is liable to be caused between one major surface and the other major surface of the non-sintered ceramic body, generating a concave warp on the major surface side that is able to largely contract when no pressure is applied during firing.
Japanese Unexamined Patent Application Publication Nos. 5-503498 and 9-92983 disclose the methods in which constraint ceramic green sheets are adhered onto both major surfaces of the multilayer ceramic body in order to limit the degree of warp of the ceramic multilayer substrate within a given range, and the multilayer ceramic green sheet is fired while optionally applying a uniaxial load along the vertical direction (Z-direction) of the multilayer ceramic body. The multilayer ceramic body should be pressed with or through porous plates in the treatments as described above, so that volatilization of organic binders contained in the multilayer ceramic body and constraint ceramic green sheets are not blocked.
However, a special equipment for firing under a load is also required in the method described above as in the methods as hitherto described, leaving some problems in the facility cost and production efficiency. In addition, since the non-sintered ceramic body is forcibly pressed using a porous plate, portions suffering a load and not suffering a load are distributed on the surface of the multilayer ceramic body with fine pitches corresponding to the pores on the porous plate, causing fine projections and depressions with the foregoing pitches on the ceramic multilayer substrate obtained.
To overcome the above described problems, preferred embodiments of the present invention provides a method for readily and efficiently manufacturing a ceramic substrate having an excellent dimensional accuracy by suppressing deformation of the substrate such as warp of the substrate.
One preferred embodiment of the present invention provides a method for manufacturing a ceramic substrate having conductor patterns, comprising: adhering a first constraint layer on a first major surface of a non-sintered ceramic body, the first constraint layer being mainly composed of a first inorganic powder that is not sintered under the sintering condition of the non-sintered ceramic body; adhering a second constraint layer on a second major surface of the non-sintered ceramic body, the second constraint layer being mainly composed of a second inorganic powder that is not sintered under the sintering condition of the non-sintered ceramic body; and removing each of the first and second constraint layers after firing the non-sintered ceramic body under the sintering condition of the non-sintered ceramic body; wherein the first constraint layer and the second constraint layer are made to have different rigidity one another.
According to the above, since the first constraint layer and the second constraint layer are made to be the layers having different rigidities one another in the foregoing non-contraction process, the rigidities of the first constraint layer and the second constraint layer may be selected so as to suppress deformation of the ceramic substrate caused by firing. Accordingly, the ceramic substrate having an excellent dimensional accuracy can be easily and efficiently obtained by suppressing deformation of the substrate such as warp of the substrate, along with suppressing firing contraction along the directions on the substrate plane.
Preferably, the first constraint layer is made to have a higher rigidity than the rigidity of the second constraint layer, in order to allow the first constraint layer to adhere on one major surface side that is able to be largely contracted by firing. Since the first constraint layer having a higher rigidity is allowed to adhere on one side of the major surface that may be largely contracted by firing, warp and distortion of the substrate ascribed to the difference of the degree of contraction between one major surface side and the other major surface side can be sufficiently suppressed. This mean that the ceramic green sheet having an excellent dimensional accuracy can be, readily and efficiently manufactured without using any special firing equipment by sufficiently suppressing deformation of the substrate.
The phrase xe2x80x9cthe constraint layer having a high rigidityxe2x80x9d as used herein refers to a constraint layer having a large deformation resistance against the non-sintered ceramic body during firing. The phrase xe2x80x9cone major surface side that is able to be largely contracted by firingxe2x80x9d refers to a side where wiring patterns are highly integrated, a side having an early onset temperature of contraction of the ceramic layer, or a side having a larger shrinkage ratio of the ceramic layer with respect to the center face located at an equal distance from one major surface side and the other major surface side of the non-sintered ceramic body. The one major surface side described above also corresponds to the side where concave warp may be caused after firing when no constraint layer are formed or when rigidity of the constraint layer is insufficient.